This invention relates to check-valves and, more particularly, to a center flow check valve of the diaphragm type for use with liquids and gases.
Check valves for a variety of different applications are well known. The purpose of a check valve is to allow fluid flow in one direction only. In the medical field, it is advantageous to include one or more check valves in a tubing set used during intravenous infusion of fluids to a patient. Such fluids often include drugs. It is therefore desirable to limit the size of the check valve in order to minimize the volumn of fluid containing the drugs which fills the valve and is generally thrown away with the valve.
Samples of various check valve designs are described in U.S. Pat. No. 4,749,003 of Leason, U.S. Pat. No. 4,222,407 of Ruschke et al, U.S. Pat. No. 3,889,710 of Brost, U.S. Pat. No. 4,415,003 of Paradis et al, U.S. Pat. Nos. 4,246,932, 4,310,017 and 4,535,820 of Raines, and U.S. Pat. No. 4,610,275 of Beecher.
As disclosed in many of these patents, it is very common in a check valve to use a flexible diaphragm (often called a disk) to seal off a flow path through the valve body in order to prevent backflow.
One problem often encountered in using a diaphragm in a check valve is difficulty in keeping the diaphragm properly positioned in relation to the flow path and the sealing surface against which it is to act. One solution to this problem has been to provide a hole in the diaphragm through which a mounting pin extends, holding the disks against transverse movement. Another solution has been to form the pin as a part of the diaphragm and insert the pin into a diaphragm mount during manufacture. In known designs of these types, however, the flow pattern through the valve cannot truly be centered around the diaphragm, because the mounting pin extends in some manner from the central portion of the valve body. In addition, the extra structure represented by the pin and its mounting represents increased material, manufacture and assembly cost. As a class, diaphragm valves suffer from sticking, disk distortion, disk deterioration during use, and improper disk placement.
Another known type of check valve is the duckbill valve, so-called because it includes elements made of silicone rubber that are assembled in opposed fashion so as resemble the bill of a duck (or, more accurately, so as to resemble the reed of a double reed musical instrument). To form the assembly, a member of silicone rubber is folded over to provide a fluid passage, and the fold is cut to provide an exit. Forward flow proceeds from within the assembly through the cut, and back flow tends to press the two members together, closing the opening formed at the cut.
One difficulty of duckbill valves is that the elements, being made of silicone rubber, tend to "heal" or grow together at the cut. This occurrence increases the pressure required to open the valve. Duckbill valves also tend to suffer from incomplete closing against back flow pressure, the result of imperfect cutting during manufacture that removes chunks of silicone. Although both diaphragm type valves and duckbill valves can be very sensitive and operate at low pressures both in the forward flow direction and in the back flow direction, they have not achieved such results consistently. In both cases, pressures required to open the valve, once it begins to malfunction, can typically reach twenty inches of water and can go as high as thirty six inches of water.